Electric Vehicles (EV)—i.e. vehicles propelled by one or more electric motors—are powered by large, rechargeable batteries. Electric vehicles are limited by available battery technology, which limits the range per charge for most of these vehicles. For widespread deployment and use of electric vehicles to be feasible, there must be widely available recharging stations, such as in homes and public locations.
Electric Vehicle Supply Equipment (EVSE) includes chargers and charging stations for electric vehicles. The EVSEs regulate the amount of power that an electric vehicle draws from the charging station. An electric vehicle is connected to a cable from the EVSE using a special connector, such as an SAE J1772-compliant connector, for recharging. A typical SAE J1772 charging cable incorporates five conductors: two for AC or DC power (AC/DC mains), one for proximity detection, one for the pilot control signal (“pilot wire”), and one for equipment ground. The control pilot carries a ±12V PWM signal to provide information to the EV such as charging level. When the electric vehicle is connected to the EVSE, the pilot wire is used to regulate the electricity available to, and/or drawn by, the electric vehicle. Pulse Width Modulation (PWM) control signals may be carried on the pilot wire between the EVSE and the EV. The PWM signal indicates to the electric vehicle whether it should recharge by drawing power from the 120 V AC line, or the 240 V AC line, for example.
The EVSE is also coupled to a power line network, such as an electrical distribution network for a home, and regulates the electricity drawn by the electric vehicle from the power line network. Power Line Communications (PLC) are used on some power line networks to transmit data and communication signals. Because the electric vehicle is coupled to the power line network via the EVSE cable, power line communications may be routed between the electric vehicle and modems on the power line network, such as modems or controllers for a utility company.
To avoid development of a new charging cable, the EV and the EVSE must communicate reliably without adding new wires to the J1772 cable. Two solutions have been considered for EV-EVSE communications: (1) communications over the AC/DC mains wires, and (2) communications using the control pilot/equipment ground.
The pilot wire provides a more benign communication environment than the AC/DC mains and offers more reliable communications and at higher bit rates. The useable bandwidth may be restricted on the AC/DC mains. For example, communications on the mains is limited to the CENELEC B, C and D band frequencies in some countries. The pilot wire is not subject those bandwidth restrictions; however, the pulse widths on the pilot wire are critical for EV-EVSE communications and must be maintained per the J1772 specification. Therefore, PLC on the pilot wire must not distort the PWM signal.
A key requirement for communication between the EVSE and the EV is to maintain a stringent round-trip latency requirement on the order of 25 milliseconds for certain DC messages or commands. However, this strict latency requirement is difficult to meet for other communications, such as EV to Utility company communications over the power grid.
Communications between the EV and the Utility may be Orthogonal Frequency-Division Multiplexing (OFDM) signals that comply with a PRIME (Powerline Related Intelligent Metering Evolution), G3 , IEEE P1901.2 or other Power Line Communication (PLC) standard, for example. The communication signal may be Frequency Shift Keying (FSK) or Phase Shift Keying (PSK) signals depending on the transmission method. Power line communication systems based on narrowband OFDM (NB-OFDM) are being developed for smart grid technologies. European utilities, such as Iberdrola (PRIME) and ERDF (G3), are pioneering the deployment of NB-OFDM PLC systems for advanced metering. The SAE and the ISO have shortlisted NB-OFDM systems that are based on PRIME and G3 for car charger applications. However, when deployed in an electronic vehicle charging scenario, these OFDM signals must not interfere with the PWM control signals exchanged between the EV and EVSE.